import gleam/string
import gleam/list
import glance.{
  type Module as AST, Definition, Function, Import, Module as AST, Public,
  UnqualifiedImport,
}
import internal/fs.{ModuleFullName}
import gleam/option.{None, Some}
import internal/ast.{AnotherFilesAst, FileAst}

const main_fun_name = "main"

pub type PublicFun {
  PublicFun(String)
}

type ModuleName {
  ModuleName(String)
}

type ImportedInfo {
  ModuleImported(ModuleName)
  FunctionImportedAsAlias
}

pub fn public_funs(file_ast) {
  let assert FileAst(ast) = file_ast
  let assert AST(_, _, _, _, _, _, funs) = ast
  use fun_def <- list.flat_map(funs)
  let assert Definition(_, Function(fun_name, is_public, ..)) = fun_def
  case is_public {
    Public if fun_name != main_fun_name -> [PublicFun(fun_name)]
    _ -> []
  }
}

pub fn is_pub_fun_used(files_ast, pub_fun_name, module_full_name) {
  let is_used_somewhere = {
    let assert AnotherFilesAst(files_ast) = files_ast
    use file_ast <- list.find_map(files_ast)
    let assert FileAst(ast) = file_ast
    let assert AST(imports, _, _, _, _, _, fns) = ast
    let imported_info_list =
      function_imported_info(imports, module_full_name, pub_fun_name)
    use imported_info <- list.find_map(imported_info_list)
    case imported_info {
      FunctionImportedAsAlias -> Ok(Nil)
      ModuleImported(module_name) -> {
        use fun_def <- list.find_map(fns)
        let assert Definition(_, Function(_, _, _, _, statements, _)) = fun_def
        check_fun_usage(statements, pub_fun_name, module_name)
      }
    }
  }
  case is_used_somewhere {
    Ok(Nil) -> True
    Error(Nil) -> False
  }
}

fn check_fun_usage(statements, pub_fun_name, module_name) {
  let assert PublicFun(pub_fun_name) = pub_fun_name
  let assert ModuleName(module_name) = module_name
  use statement <- list.find_map(statements)
  case
    statement
    |> string.inspect
    |> string.contains(
      "FieldAccess(Variable(\""
      <> module_name
      <> "\"), \""
      <> pub_fun_name
      <> "\")",
    )
  {
    True -> Ok(Nil)
    False -> Error(Nil)
  }
}

fn module_full_name_to_module_name(module_full_name) {
  let assert ModuleFullName(module_full_name) = module_full_name
  let assert Ok(module_name) =
    string.split(module_full_name, "/")
    |> list.last
  ModuleName(module_name)
}

fn function_imported_info(imports, module_full_name, pub_fun_name) {
  list.filter_map(imports, fn(imp) {
    case imp {
      Definition(_, Import(import_name, module_alias, _, aliases))
        if ModuleFullName(import_name) == module_full_name
      ->
        case
          list.any(aliases, fn(alias) {
            let assert UnqualifiedImport(fun_name, _) = alias
            PublicFun(fun_name) == pub_fun_name
          })
        {
          True -> Ok(FunctionImportedAsAlias)
          False ->
            Ok(
              ModuleImported(case module_alias {
                Some(alias) -> ModuleName(alias)
                None -> module_full_name_to_module_name(module_full_name)
              }),
            )
        }
      _ -> Error(Nil)
    }
  })
}